The art of collection and conversion of solar radiation into directly usable sources of energy is well known. Practical demonstrations have been effected with increasing frequency. However, amortization of the initial costs of the devices required have made widespread application uneconomical. The instant invention relates to a more efficient solar radiation collector, a principal component of any solar energy conversion system.
Highly efficient collectors could be made, of economical construction, if the radiation source and the radiation collector remained in a fixed positional relationship. However, the rotation of the earth on its own axis creates a constant daily movement of the collector with respect to the sun's rays, and the rotation of the earth around the sun causes an annual movement of the collector with respect to the sun's rays equivalent to twice the angle of inclination (about 23.degree. 30') of the earth's axis from an axis perpendicular to the earth's orbit (ecliptic) around the sun. Thus, a fixed collector receives the sun's rays at continuously changing angles as a function of the time of day and day of the year. Collectors tilted so as to be perpendicular in plane to the sun's rays at noon on summer solstice, would have a plane 47.degree. off of a perpendicular to the sun's rays at noon on winter solstice.
A variety of means to overcome this initial problem in utilizing solar radiation have been devised. One basic approach has been to mechanically move the solar collector or solar reflector to "track" the sun, so that a maximum amount of the radiation flux incident upon the system would be utilized. Drescher (U.S. Pat. No. 3,171,403 in 1965) taught a solar heating system requiring a mechanical tracking means. See also U.S. Pat. Nos. Phelps (2,969,918 in 1961), Falbel (3,841,302 in 1974), Blake (3,892,433 in 1975), Jahn (3,905,352 in 1975), Anderson (3,924,604 in 1975), and Barber (3,980,071 in 1976). Northrup (3,991,741 in 1976) taught the use of directional optics with moving absorbers following the changing focal points of received radiation. Also teaching use of optics was Fletcher, et al. (U.S. Pat. No. 3,915,148 in 1975), using Fresnel lenses which were fixed. Edlin (U.S. Pat. No. 3,058,394 in 1962) taught a fixed array of light reflective surfaces of a parabolic profile, having a collector at the focal region of the various parabolas. The principal objection to the solutions outlined above is the complexity of the devices required and attendant high cost. Illustrative is the invention of Davis (U.S. Pat. No. 3,957,030 in 1976), which would be highly adaptable to space craft, where economy is not necessarily of high priority. Falbel (U.S. Pat. No. 3,923,039 in 1975) taught a fixed, scoop-shaped device, particularly useful in vertical surfaces.
Another problem encountered in the conversion of solar radiation is the relatively low temperatures at which the absorbing collector transfers the radiated energy by conduction to the heat transfer liquid. The production of temperatures required for refrigeration or space cooling systems by the absorption process can be accomplished only very inefficiently by the absorption of solar flux at atmospheric concentration. Therefore, to be effective the amount of flux incident upon a system must be concentrated to increase heat transfer temperature differences and reduce the convection heat loss of the collectors. The solution of the requirement for flux concentration closely parallels the solution to the sun tracking requirement, and some of the solutions are included in the prior art cited above. The prior art solutions are generally characterized by sophisticated and expensive optics or reflectors of complex curvature.
The present invention overcomes much of the difficulty previously experienced by selectedly positioning simple rectangularly shaped planar reflectors and rectangularly shaped planar collectors. Both the reflector and collector materials are well known and have been used in solar energy technology; however, their use has been at an efficiency generally not great enough to allow the use of solar radiation for refrigeration or space cooling. In prior art, a simple array has been used whereby the axes of the collectors were oriented in the east and west direction, the collectors tilted from the north-south horizontal. This angle of tilt in a standard geometrical array varied with the latitude of the place where the system was installed so that during the season in which the greatest efficiency was desired, the collector would be in a plane approximately perpendicular to the sun's rays. Instead of having one large panel collector, several narrower ones have been desirable so that there will be a lower profile on roof surfaces where they are normally situated; however, in this preferred array, the southern most panels (in the northern hemisphere) shadowed the northern most panels at winter solstice, or a large unheated gap would be unutilized between panels at other sun positions during the other seasons. Thus, in the most economical collector system, the total solar flux incident upon the system could never be utilized because of compromises in collector height, angle, and spacing which had to be made to make a year-round system of maximum efficiency. Using reflectors between the spaced tilted collectors, the reflectors connecting the northern upper edge (in the northern hemisphere) of one collector with the lower southern edge of the adjacent northerly collector, additional flux can be retained, and to some extent concentrated. However, with flat reflectors just described, flux is still reflected back into the atmosphere during a considerable portion of the year. It should be noted here that solar radiation consists of direct beams from the sun plus diffuse radiation due to refraction and reflection of direct beams by atmospheric and terrestrial interference.
My invention, called the Espy Geometry, consists in the array or arrangement of multiple flat panels of solar radiation collectors, with long axes horizontal in the east-west direction, and the plane of the reflector tilted from the horizontal in the north-south direction. These collector panels are alternately spaced with multiple faceted reflectors comprising two or three planar rectangularly shaped reflectors tilted at angles such that no shadows fall on the system during the mid-day hours at any time during the year, and all of the flux incident upon the system as a whole is directly or indirectly made incident on the collectors. Compared with the use of standard collectors alone, or with single faceted reflectors and collectors, the efficiency of my invention is considerably greater. The increased efficiency, with cheap components, enables the heat transfer liquid to attain temperatures in the range where refrigeration or space cooling can be effected by the use of the absorption process. The arrangement allows total flux utilization in the heating season, with relatively lesser flux concentration, an acceptable situation when the system is used for heating. However, as the season progresses to summer solstice, the flux is collected at greater concentrations for the use of the system in the refrigeration or space cooling mode.